There's a new video on the Car Wizard's YouTube channel on replacing the heater core on a 2001 Chevy Avalanche, and it is the automotive equivalent of open heart surgery. An unbelievable number of parts have to be removed to get to the heater core. In the video you get to see the top and bottom of the entire heater box as in the article photos, too. Rob took the prudent path on this repair.
Is your issue mouse related or did it come that way from the factory? Maybe talk with your insurance company to see if you can file a claim. That’s too nice a car to let sit.
No, the car was fine until the pandemic hit and it went unused for a while in the early days when we were kind of locked down and not really going anywhere. That's when (I assume) a mouse crawled up in there somewhere and died. That or it's gotten moldy in there, but it smells more like dead something. I don't have a problem paying for repair; the problem is I live in a small city where the local Chevy dealer's service department is incompetent and uninterested in actual, you know...service.